Greece has hired Deutsche Bank and Morgan Stanley to conduct a voluntary buy back of its debt, a senior finance ministry official told Reuters on condition of anonymity on Wednesday.

"At this moment, we intend the buy back to be voluntary," the official said. "We hope that early next week, if possible on Monday, the Public Debt Management Agency (PDMA) will publish the invitation for the buy back," he added.

Eurogroup finance ministers and the International Monetary Fund (IMF) agreed earlier this week to conduct the buy back by mid-December, as part of measures to make Greece's debt sustainable.

Greece has not determined yet at which price it will offer to buy back the debt from private bondholders, the official said.

Concerns that the buy back would be imposed on Greek banks have led their shares to plunge since Tuesday, when the plan was announced.